Daylighting performance of tubular solar light pipes: measurement, modelling and validation.

The innovation of natural daylighting light pipes took place more than twenty years ago. Since then its daylighting performance has been reported in a number of studies. To date, however, no mathematical method that includes the effect of straight-run and bends within light pipes has been made available. Therefore, a general mathematical model for light pipes is desirable to assess and predict its daylighting performance. Furthermore, such a general model can enable the assessment of light pipe systems' efficiency and potential in energy saving. A modified form of daylight factor, Daylight Penetration Factor (DPF), has been introduced to build a sophisticated model that takes account of the effect of both internal and external environmental factors, and light pipe configuration. Measurements and mathematical modelling activities aimed at predicting the daylighting performance of light pipes with various configurations under all weather conditions in the UK were undertaken. A general daylighting performance model, namely the DPF model, for light pipes was developed and validated. The model enables estimation of daylight provision of the light pipes with a high degree of accuracy, i.e. R² values of 0.95 and 0.97 for regression between predicted and measured illuminance were respectively obtained for the model. The DPF model uses the most routinely measured radiation data, i.e. the global illuminance, as input. Considering that in real applications, light pipes installed in a particular building may not receive the full amount of global illuminance as measured by a local meteorological office, this may be due to partial shading of the light pipe top collector dome. Therefore, to enable the application of the DPF model in practical exercises, fundamental work on sky diffuse illuminance measurements has been undertaken. An exhaustive validation has been carried out to examine the DPF model in terms of the structure of the model and its performance. The DPF model was compared against studies by other independent researchers in the field. Independent data sets gathered from a separate site were used to validate the performance of the DPF model. Comprehensive statistical methods have been applied during the course of validation. Relevant, brief economic and environmental impact assessments of the technology under discussion have also been undertaken. One of the main achievements of this work is the mathematical method developed to evaluate the daylighting performance of light pipes. The other main achievement of this work is the development and validation of the DPF models for predicting light pipes' daylighting performance.